1. Field of the Invention
The present invention relates to an original holding plate hinging mechanism for a copying machine, a printing machine or the like.
2. Description of the Prior Art
A copying machine has a soft and flexible original holding plate, such as a rubber plate, or a hard original holding plate, such as a synthetic resin plate.
The former is capable of covering the upper surface of the original satisfactorily even if the original is a thick original such as a book. Therefore this flexible holding plate has less possibility of allowing external light to leak into the optical system disposed within the body of the copying machine, which secures making a clean copy to advantage. However, the flexible holding plate has disadvantages because the flexible holding plate is incapable of being held at a half-open position without any assistance, and hence is unsatisfactory in respect of accessibility in changing originals. Recently, the latter, namely, a hard original holding plate, which is capable of being held at a half-open position with a hinging mechanism, has become widely employed.
When holding a thick solid original, the latter, namely, the hard holding plate, is tilted against the original if the hard holding plate is hinged simply, hence the hard original holding plate is incapable of applying pressure uniformly to the original to press the same against the contact glass and shielding the optical system for external light. Accordingly, such a hard holding plate is hinged to the frame of the copying machine with a hinging mechanism including a lifting means so that the holding plate is placed practically in parallel to the surface of the original when closed.
This is shown in FIGS. 1 to 3. In one arrangement, a lifting means including a swing member 2 attached pivotally to a bracket 1 attached to the upper part of a copying machine frame A, a supporting member 3 attached pivotally to the swing member 2, a supporting frame 4 extending from the supporting member 3, and an original holding plate B supported pivotally practically at the middle of the opposite sides thereof on the supporting frame is, as shown in FIG. 1, large in size and has a disadvantage that the holding plate B is unsteady during opening and closing operation and moves laterally.
In another lifting means including a supporting member 6 attached pivotally to a bracket 5 attached to the upper part of a copying machine frame C, a lifting member 7 attached pivotally to the free end of the supporting member 6 so as to be rotatable in the same direction as the rotation of the supporting member 6, and an original holding plate D attached at one end thereof to the lifting member 7 has, as apparent from FIG. 2, disadvantages that the unstable lifting member 7 detriorates the accessibility of the holding plate D and the mechanism is unable to hold the holding plate D stably at the open position.
As shown in FIG. 3, a further lifting means including a supporting member 9 is attached pivotally to a bracket 8 attached to a copying machine frame so that the supporting member 9 turns reversely to the opening-closing direction of turning of a holding plate F, a lifting member 10 holding the holding plate F and attached pivotally to the free end of the supporting member 9, and a magnet 11 disposed to attract the free end of the supporting member 9 magnetically toward the copying machine frame E has disadvantages that reversing the supporting member 9 to place the holding plate F horizontally over a solid original needs a fairly large force if the magnetic attraction of the magnet 11 is excessively large, while the holding plate F is placed unstably if the magnetic attraction of the magnet 11 is insufficient, the magnet 11 needs to be strong and hence expensive, and the magnet 11 is subject to breakage.